1. Field of the Invention
The present invention relates to synthetic lubricating oils useful as base stock(s)/base oil(s) per se, as lubricating oil blending components or as additives.
2. Description of the Related Art
Modern engines and other equipment such as gears, transmissions, differentials, compressors, hydraulic equipment, turbines, marine diesels etc. are designed for higher operating temperatures, lower friction, closer machined parts tolerances, and longer periods between servicing, e.g., between lubricant changes.
Such requirements put demands on the lubricating oil which cannot be easily met by traditional mineral oil based lubricants even when highly additized. Mineral oil based lubricants when employed in such high stress environments experience coking, high evaporative loss and insufficient load-carrying performance.
The new performance criteria have led to the development of synthetic lubricants such as polyalphaolefins, alkylated aromatics, alkyl ester stocks, polyol ester stocks and polyphenyl ether.
Polyol esters have good thermal and oxidative stability and low temperature properties but are subject to hydrolysis at high temperature in wet environment, leading to acid production which causes metal corrosion, an increase in lubricant viscosity and a consequential decrease in lubricant service life.
Alkylated aromatics (e.g., alkylated benzene, alkylated naphthalene, alkylated biphenyl etc.) do not hydrolyze and provide very good low temperature properties, excellent solvency, good elastomer compatibility and very good oxidation stability. Alkylated naphthalene has been found to be the alkylated aromatic of choice for use as base stock or blending stock with, e.g., polyalphaolefin to provide significant performance improvements in oxidation stability, solubility, elastomer compatibility, additive solvency and hydrolytic stability (see U.S. Pat. No. 5,602,086). U.S. Pat. No. 5,254,274 discloses the alkylation of aromatic compounds with C20 to C1300 olefinic hydrocarbon using acidic alkylation catalyst.
Polyphenyl ethers are also known in the art and have higher operating temperatures than other synthetic base stocks but are also characterized by high cost and poor low temperature properties which have limited their usefulness. U.S. Pat. No. 3,451,061 discloses the preparation and use of polyphenyl ethers as functional fluids.
Synthetic lubricating base stock(s)/base oils such as polyalphaolefins are low solvency hydrocarbons because they comprise 100% isoparaffins and 0% aromatic hydrocarbons. Similarly, hydroisomerized or hydrodewaxed waxy hydrocarbons such as slack waxes (i.e., waxes recovered from lubricating oil stocks by solvent dewaxing), waxy raffinate and especially Fischer-Tropsch wax hydroisomerized or hydrodewaxed base oils (also referred to as Gas-to-Liquids (GTL) base stock(s)/base oil(s)) are also highly paraffinic and, depending on the wax source, as in the case of hydroisomerized/isodewaxed Fischer-Tropsch wax base stock/base oil, have essentially zero percent aromatics and/or hetero-atom components present and are also characterized by low solvency for solubilizing additives.
U.S. Pat. No. 5,520,709 relates to alkyl ethers of sulfur-containing hydroxyl-derived aromatics that have been found to be effective as high performance synthetic lubricant base stocks with superior catalytic thermal/oxidative stabilities, excellent antiwear and load-carrying properties, as exemplified by bisphenol sulfide based products. These ethers are also highly useful in fuel compositions. In view of some industry specifications limiting the sulfur content in finished lubricants, the presence of sulfur in the molecule and the high cost of the 4,4′-thiodiphenol might limit its utilization of alkyl ethers of sulfur-containing hydroxyl-derived aromatics.
U.S. Pat. No. 5,368,759 discloses an ester-containing reaction product of a carbonyl compound, preferably an acyl halide and a thiodiphenol has high temperature antioxidant properties. The reaction product is useful as synthetic lubricant base fluid or as antioxidant additive when used in minor amounts of 0.01 to 10 wt % in a mineral oil or hydrocracked oil lubricant base fluid. The reaction product can be used in a fuel.
JP 2000 169867 discloses a refrigerating oil composition containing a coolant based as C1-C8 hydrocarbons and a polyether of the formula:R1—((OR2)m—OR3)n wherein R1 is an n-valent group having an aromatic nucleus R2 is a C2-C6 polymethylene with one or more hydrogen atoms optionally substituted with a C1-C20 alkyl group or a group having the formula —R4—(OR5)p—OR6 wherein R4 is methylene or ethylene, R5 is C2-C6 polymethylene with one or more of hydrogen atoms optionally substituted with a 1-20 carbon alkyl group, R6 is a 1-10 carbon alkyl group or hydrogen, p is 0 to 80, R3 is a 1 to 10 carbon alkyl group or hydrogen n is 1 to 6 and m is a number giving a product of m times n of 3 to 80.
U.S. Pat. No. 5,750,480 discloses a hydrolytically stable lubricating oil exhibiting anti-wear properties, dispersancy, thermal and oxidative stability and a method for producing the lubricating oil. The lubricating oil is a mixture of mono-di- and tri-alkylated anisole having the formula
wherein R1, R2 and R3 are hydrogen or a secondary alkyl radical containing 8 to 24 carbon atoms provided all three of R1, R2 and R3 cannot be hydrogen.
JP 3370829B teaches a lubricating oil composition containing a base oil an additive and 0.2 to 8 wt % of a mixed anti-oxidant comprising dialkyldithiocarbamate and aromatic amine. The base oil can be a mixture of polyolesters and alkyl phenyl ether oil. The lubricating oil can also be turned into a grease by addition of thickeners. The alkyl phenyl ether oil can be alkyl diphenyl ether, alkyl polyphenyl ether, dialkyl tetraphenyl ether and the like.
EP 0 466 307 is directed to synthetic lubricant base oils comprising oligomers prepared by reacting over a catalyst a C10 to C24 linear olefin with an alkyl substituted diphenyl, diphenyl ether or anisole.
EP 0 438 709 teaches an engine oil containing up to 10 wt % of an alkylphenol alkoxylate, or of a bisphenol alkoxylateR1[O(R2O)nH]m  I
wherein R1 is a radical of an alkylphenol having up to 2 alkyl groups of 6 to 24 carbon atoms or a bisphenol, R2 is the radical of butylene oxide alone or a mixture with propylene oxide, n is from 10 to 1000, and m is 1 or 2. When R1 is Bisphenol A the product can be the material of Formula II (provided m is 2).
JP 57012097 teaches a base oil for lubrication of metal containing polyoxyalkylene ether of Bisphenol A or Bisphenol B, i.e., materials of the formula
The base oil is described as having numerous advantages, including no generation of sludge, being non-corrosive to rubber and metal, having a relatively high flash point, high viscosity index, soluble in water, low toxicity, superior heat resistance.
U.S. Pat. No. 4,256,596 teaches a composition useful as lubricant or fuel additive produced by the oxidative coupling of a mixture of (a) at least one hydroxy aromatic compound containing no aliphatic substituents with more than 4 carbon atoms and (b) at least one hydroxyaromatic component containing at least one aliphatic substituent with at least 12 carbon atoms. At least one position ortho to an OH group in each of (a) and (b) must be unsubstituted. Each of (a) and (b) further contain X and Y groups which can be H, halo, R, ROH OR, SR, RCl wherein R is up to 4 carbons.
U.S. Pat. No. 3,451,061 teaches poly(m-oxyphenylene) benzenes a functional fluid. The materials are unsubstituted aromatic ethers of the general formula

U.S. Pat. No. 3,060,243 teaches the preparation of materials of the formula 2,2-bis(para-alkenyloxyphenyl) propane

U.S. Pat. No. 2,560,350 teaches 2,2-bis(para alkyloxyphenyl) propane as an insecticide.
U.S. Pat. No. 2,504,382 teaches miticidal compositions comprising 2,2-bis(para-alkoxyphenyl) propane, which are materials of the formula
wherein Rs are alkyl groups containing from 1 to 4 carbon atoms.